a) \(\left(19x+2\cdot5^2\right):14=\left(13-8\right)^2-4^2\)
\(\left(19x+2\cdot5^2\right):14=9\)
\(19x+2\cdot5^2=9\cdot14=126\)
\(19x+50=126\)
\(19x=126-50=76\)
\(x=\frac{76}{19}=4\)
b) \(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\)
\(\left(x+x+..+x\right)+\left(1+2+3+...+30=1240\right)\)(31 chữ số x)
\(31x+\frac{30\cdot31}{2}=1240\Leftrightarrow31x+465=1240\)
\(31x=1240-465=775\)
\(x=\frac{775}{31}=25\)
c) \(11-\left(-53+x\right)=97\)
\(11+53-x=97\Leftrightarrow64-x=97\)
\(x=64-97=-33\)
d) \(-\left(x+81\right)+213=-16\)
\(-x-81+213=-16\)
\(-x+132=-16\)
\(-x=-16-132=-148\)
\(x=148\)
..........
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